The invention concerns an electret condenser microphone (ECM) with a new simplified housing construction. Miniature ECMs are currently in widespread use in portable communication terminals and computing devices for consumer and professional applications. ECMs are capacitor microphones which rely on a permanently charged electret layer arranged on the back plate of the ECM to provide a DC bias voltage for the capacitive transducer element. The permanently charged electret layer can for example be a Teflon layer wherein electrical charges are injected and permanently trapped. Miniature ECMs are sold in very large quantities for numerous highly cost-sensitive consumer applications which make costs considerations very important. Measures that can be taken to reduce manufacturing costs for example in terms of utilized manufacturing technology, manufacturing operations and component costs are accordingly of great interest and importance.
U.S. Pat. No. 5,272,758 discloses an ECM which comprises a cylindrical metallic housing or capsule. The cylindrical microphone housing comprises an integrally formed top plate or lid having a plurality of through-going sound holes. The inner surface of the entire cylindrical housing, including the top lid, comprises an electret polymer film. A conductive diaphragm is mounted to a cylindrical metallic diaphragm holding member in spaced relationship to the back plate in the top lid. The electret polymer film establishes electrical contact to wire traces on the bottom portion of the wiring board or substrate whereon an IC device is attached. The cylindrical metallic diaphragm holding member is used to establish electrical contact between the conductive diaphragm and the IC device through wire traces on the wiring board.
U.S. 2009/0268930 A1 discloses an ECM with a cylindrical metallic housing or capsule. A conductive diaphragm is mounted to a cylindrical metallic ring or carrier. A perforated back plate comprises an electret layer facing outwardly of the ECM relative to the conductive diaphragm. Electrical connection in vertical direction between the conductive diaphragm and a FET amplifier, mounted on a PCB carrier, is established by an electrical conductive ring contacting a wire trace on the PCB carrier. An opposite surface of the electrical conductive ring contacts the cylindrical metallic ring functioning as a diaphragm holder. Vertical electrical contact between (ground of) the FET amplifier and the back plate is effected through the cylindrical metallic housing.
U.S. Pat. No. 8,043,897 B2 discloses MEMS microphones and MEMS microphone packages and assembly methods for production of the latter in batches.
Accordingly, there is a need in the art for improved ECMs which can reduce manufacturing costs without sacrificing important performance metrics such as electroacoustic sensitivity, frequency response, noise level and housing volume. ECMs in accordance with the present invention provide numerous advantages such as lower parts count, simplified assembly process, enlarged back chamber volume etc. Furthermore, a housing structure of the present ECM may be built by a reduced number of separate components fabricated by the application of printed circuit board technology to take advantage of the sophisticated capabilities and low cost of today's printed circuit board technology.